One of the materials available for postemergence crabgrass control in turf is Acclaim Extra. The following is more information.
Acclaim Extra: The recommended use rate of Acclaim Extra is highly dependent on turf grass species and growth stage of crabgrass. Consult the label carefully, especially for use on bentgrasses. Although the label states that 28 oz/A may be used on well established Kentucky bluegrass, I generally do not recommend exceeding 20 oz/A. Tall and fine fescue as well as perennial ryegrass are very tolerant to Acclaim Extra. At 20 oz/A Acclaim Extra is effective on crabgrass up to 2 tillers. However, under favorable environmental conditions, I have observed that this rate can control crabgrass up to 3-4 tillers. Tank-mixing or applying Acclaim Extra prior to or following a broadleaf weed herbicide application (especially herbicides containing 2,4-D and/or MCPP) may reduce weed control. Although the formulation contains a built in spray adjuvant system, depending on application equipment the addition of non-ionic surfactant (NIS) may be recommended.
Information from Dr. Stephen E. Hart, Associate Extension Specialist, Rutgers University.